I had a 2005 2x4 4Runner 4.7L towing a 17' Casita fiberglass trailer GVWR 3500lbs, 420lb tongue weight, no WDH just anti sway friction bar. 2005 was the first model year with the improved performance specifications and probably similar to yours and it had a 5 speed auto transmission. I think the tow rating was 7000lbs. We took several trips to Glacier Natl Park with this combo. Got about 13 to 14 mpg average towing with a useable range of about 225-250miles towing 60mph. While on the flatlands it was an easy tow but on some of the interstate grades between Sheridan and Billings I had to shift down to 3rd to maintain 55mph but it wasn't floored.
When we started looking at Airstreams we considered the smaller models so we could keep the 4Runner but when we decided to go for a 25 I knew a different tow vehicle would be needed as the hitch weight of the 25s approaches 1000lbs. I just couldn't imagine towing a much larger trailer with our 4Runner with the Casita experience in my mind.
2008 Classic 25fb "Silver Mistress"
2015 Ram 2500 6.7L Cummins. Crew Cab, 4x4, Silver
2010 Tundra 5.7L, Double Cab, 2wd, White